Hello. Just throwing this out there for people, everyone seems to be going pure glass cannon AD or AP on MF, regardless of the fact that she has decent on-hit damage and does rather well with a bit of tankiness.
I like utilizing ALL of a champion, not just one or two skills or attributes. Enjoy. ^^
The other builds are interesting, but not really to be taken as serious as the main one.

Decent damage most the game, but doesn't really get much defense until the per level runes begin taking effect and the last two defensive items are obtained.

Overall, quite balanced.

I know it's odd, but I try and maximize damage. Remember, I'm trying to utilize a mix of AD and on-hit with tankiness.

Kind of standard for me.
For quints and marks I use offensive penetration, armor penetration here.
It's also feasible to run scaling AP for her spells and on-hit.
They're power scales with levels and items, so yours should match, in my opinion.
Armor Seals, always. Scaling is nice for late game, but flat helps you take early game over.
Scaling MR glyphs are needed.
They're power scales with levels and items, so yours should match, in my opinion. But to each their own.

As previously stated, I'm attempting to show people she can be used as more than an AD glass canon. ^_^
I just try and balance farming and damage early, and use the lantern to avoid some of the enemy ADCs damage. Later I grab a bit of hp, and then lastly up my defense with Tabi and Merc. Scimi.
If you want more tankiness over damage, swapping a trinity for a Warmogs is possible, but I don't suggest it. Trinity is just god-like on MF.
I like Malady on her all game, but for a more crit-oriented build you can grab the Shiv or PD.

I skill her on-hit first, then her Q for harass. Only use her Q if you can land the second hit on a champ.

Her pool is more for utility, though with this build it should do a bit more than standard ADC MF.

Obviously prioritize leveling her ultimate above everything. Once again, it'll do a bit more with the AP in here.